The present invention relates to a molding resin composition, and more particularly relates to a molding resin composition of polyimide which is excellent in high-temperature stability, chemical resistance and mechanical strength as well as processing ability in molding.
Polyimide has so far been excellent in mechanical strength and dimensional stability in addition to high-temperature resistance Besides it has also flame retardance and electrical insulative properties. Therefore polyimide has been used in the field of electric and electronic parts, aeronautics and space instruments and transport machinery, and is also expected for a wide use in the future in the field where high temperature resistance is required.
Many kinds of polyimides which exhibit outstanding properties have been developed to date. Some types of polyimides, however, have excellent high-temperature resistance whereas they have no definite glass transition temperature and require a sinter molding method for processing them.
On the other hand, other types of polyimides have excellent processing ability whereas they have low glass transition temperatures and are soluble in halogenated hydrocarbons. They are unsatisfactory from a viewpoint of high temperature stability and solvent resistance. Thus there are both merits and drawbacks in their properties.
Accordingly polyimide has been desired which is excellent in high-temperature stability and solvent resistance and also has an outstanding processing ability as a molding material.
As to polyimide which satisfies above mentioned properties, the present inventors have found polyimide having recurring units of the following formula: ##STR6## wherein X is a sulfonyl radical or a carbonyl radical and R is a tetra-valent radical selected from the group consisting of aliphatic radical having 2 or more carbon atoms, alicyclic radical, monoaromatic radical, to condensed polyaromatic radical, and non-condensed polyaromatic radical wherein aromatic radicals are linked to one another directly or via a bridge member. (Japanese Laid-Open Patent No. TOKKAISHO 62-53388 (1987)).
The above polyimide is a thermoplastic polyimide having fluidity in high temperatures in addition to excellent mechanical, thermal and electrical properties which are in polyimide.
Compared with ordinary engineering polymers represented by polyethylene terephthalate, polybutylene terephthalate, polysulfone and polyphenylene sulfide, the polyimide is superior to these polymers in high-temperature resistance and other properties. On the other hand, the processing ability of the polyimide is still inferior to these polymers.
Generally in injection molding or extrusion molding, lower melt viscosity leads to better processing ability. For example, higher melt viscosity requires higher injection pressure in the molding stage and the molded products are subject to excessive stress thereby lowering operation efficiency and causing adverse effects on the properties of molded products. The above stated polyimide can be injection molded because it has an excellent fluidity at high temperatures. The polyimide is nevertheless required to enhance its workability.